Elastase is the only known proteolytic enzyme with the capability of degrading the protein elastin. Since this protein makes up a considerable portion of the dry weight of arterial tissue and since in vascular disease the elastic laminae appear to undergo chemical changes it is attractive to speculate that these changes occur as the result of the mediation of the enzyme elastase. These studies are designed around basic, systematic studies on the interaction of pancreatic elastase and purified serum inhibitors. It is believed that the pursuit of these studies will lead ultimately to a more clear understanding of the possible systemic role(s) of the enzyme elastase.